U.S. patent number 7,252,243 [Application Number 11/048,899] was granted by the patent office on 2007-08-07 for injection nozzle for purification.
This patent grant is currently assigned to Haldor Topsoe A/S. Invention is credited to Ingvard Bjorn, Par Gabrielsson.
United States Patent |
7,252,243 |
Bjorn , et al. |
August 7, 2007 |
Injection nozzle for purification
Abstract
Method and apparatus for uniformly injecting a fluid stream into
a gas stream at elevated temperature by means of an injection
nozzle comprising a nozzle head and a supply inner tube being
concentrically surrounded with an outer casing tube spaced apart
from the inner supply tube. It comprises passing the fluid stream
through the inner tube and the nozzle head and maintaining
temperature of the fluid stream in the inner tube by providing
thermal insulation in at least part of an annular space between the
inner tube and the outer tube. Further it comprises maintaining a
constant flow of the fluid inside the inner tube and nozzle head by
plugging the nozzle head at outlet end and spraying the fluid
stream through a number of nozzle holes provided in the nozzle head
adjacent to the outlet end of the nozzle head.
Inventors: |
Bjorn; Ingvard (Hellerup,
DK), Gabrielsson; Par (Helsingborg, SE) |
Assignee: |
Haldor Topsoe A/S (Lyngby,
DK)
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Family
ID: |
34673556 |
Appl.
No.: |
11/048,899 |
Filed: |
February 3, 2005 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20050173553 A1 |
Aug 11, 2005 |
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Foreign Application Priority Data
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Feb 5, 2004 [DK] |
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PA 2004 00175 |
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Current U.S.
Class: |
239/8; 239/416.5;
239/416.4; 239/418; 239/431; 239/434; 239/426; 239/398 |
Current CPC
Class: |
F01N
13/14 (20130101); F01N 3/2066 (20130101); F01N
2610/01 (20130101); F01N 2610/02 (20130101); F01N
3/30 (20130101); F01N 2610/08 (20130101); Y02T
10/24 (20130101); F01N 2610/1453 (20130101); Y02T
10/12 (20130101) |
Current International
Class: |
A62C
5/02 (20060101); A62C 31/00 (20060101); B05B
7/04 (20060101); B05B 7/06 (20060101); B05B
7/12 (20060101) |
Field of
Search: |
;239/8,434,434.5,431,429,423,424,418,421,416.4,416.5,424.5,426,290,291,398 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 886 043 |
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Dec 1998 |
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EP |
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2001-152831 |
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Jun 2001 |
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JP |
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WO 96/36797 |
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May 1995 |
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WO |
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WO 2004/030827 |
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Apr 2004 |
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WO |
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Primary Examiner: Hwu; Davis
Attorney, Agent or Firm: Dickstein Shapiro LLP
Claims
The invention claimed is:
1. Method of uniformly injecting a fluid stream into a gas stream
at elevated temperature by means of an injection nozzle comprising
a nozzle head and a supply inner tube being concentrically
surrounded with an outer casing tube spaced apart from the inner
supply tube, which method comprises passing the fluid stream
through the inner tube and the nozzle head and maintaining
temperature of the fluid stream in the inner tube by providing
thermal insulation in at least part of an annular space between the
inner tube and the outer tube; maintaining a constant flow of the
fluid inside the inner tube and nozzle head by plugging the nozzle
head at outlet end and spraying the fluid stream through a number
of nozzle holes provided in the nozzle head adjacent to the outlet
end of the nozzle head; spraying the fluid stream through the
nozzle holes in a direction being substantially at right angles to
flow direction of the gas stream and adjacent to center axis of the
gas stream channel; and uniformly distributing the sprayed fluid
stream into the gas stream by conically narrowing the outer casing
tube in region adjacent to the nozzle head.
2. Method of claim 1, wherein the gas stream is an exhaust gas
stream from a Diesel engine and the fluid stream is an aqueous
solution containing between 20% and 50% by weight, preferably
between 30% and 35% by weight of urea.
3. Method of claim 2, wherein the aqueous solution is passed to the
nozzle head by pressurized air.
4. Injection nozzle for use in a method according to anyone of the
preceding claims comprising a nozzle head being connected to a
fluid stream supply tube, wherein the supply tube is concentrically
and spaced apart surrounded by an outer casing tube; space between
the supply tube and the casing tube is at least partly filled with
thermal insulation material; the outer casing tube is conically
narrowed to adjacent to outer wall of the supply inner tube in
region adjacent to the nozzle head; the nozzle head is plugged at
outlet end with a plug; and the nozzle head is provided with a
number of equally spaced nozzle holes in region adjacent to the
plug of the nozzle head.
5. Injection nozzle of claim 4, wherein the sizes of outer diameter
and inner diameter of the nozzle head are identical to sizes of
outer diameter and inner diameter of the supply tube.
6. Injection nozzle of claim 4, wherein the nozzle head is a tube
equipped with a 90.degree. bend between the supply tube and the
nozzle holes.
7. Injection nozzle of claim 6, wherein the straight part of the
nozzle head between the bend and the nozzle holes has a length of 5
mm.
8. Injection nozzle of claim 4, wherein the thermal insulation
material is a ceramic compound.
9. Injection nozzle of claim 4, wherein the inner surface of the
conically narrowed part of the outer casing tube has an angle of
30.degree..
10. Injection nozzle of claim 4, wherein the supply tube has an
outer diameter of 6 mm and a wall thickness of 1.5 mm, the outer
casing tube has an outer diameter of 25 mm and a wall thickness of
1.22 mm, and the nozzle head is equipped with four equally spaced
holes each with a diameter of 0.55 mm or with eight equally spaced
holes each with a diameter of 0.39 mm.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to injection of a fluid into a gas by a
nozzle. The invention is specifically directed to injection of a
solution into a hot gas, where one specific use of the invention is
in connection with NO.sub.x removal from exhaust gas from a diesel
engine.
2. Description of Related Art
Nozzles are widely used for injection of one fluid into another,
also in connection with NO.sub.x removal from engine exhaust
gasses.
In WO 96/36797 patent application Hofmann et al. disclose injection
of urea solution/air mixture into an exhaust gas in a vehicle. The
mixture is sprayed into the exhaust gas pipe just inside the pipe
close to the pipe wall so the solution does not become too hot
before it is sprayed out in the gas. The distribution of the
injected liquid is not uniform when seen from a cross section of
the exhaust gas pipe.
Tsuneaki discloses another exhaust gas cleaning system in JP
2001152831. Here nitrogen oxides are reduced by urea solution
sprayed into exhaust gas in a vehicle too. The injection nozzle is
inserted through the wall of an exhaust gas pipe extending only a
short distance from the inner surface, which creates an uneven flow
pattern.
Kupper et al. disclose an injection nozzle for fuel in U.S. Pat.
No. 4,502,196 comprising two coaxial tubes with a narrow space
between filled with insulating material. The outer tube forms a
hood around also the tip of the nozzle in order to keep the fuel
below a temperature where formation of coke starts. The fuel is
sprayed out through one hole only through both inner tube and hood
in a coaxial direction with the nozzle.
Another gas cleaning method is described by Zauderer in U.S. Pat.
No. 6,048,510. The content of nitrogen oxides in a flue gas in a
coal fired boiler is reduced by injection of air atomised water
droplets containing dissolved urea or ammonia. The droplets are
injected where the temperature is optimal, and the size of the
droplets is adjusted to this temperature by the nozzle
construction.
However, these nozzles tend to block and none of the injections
secure a very high degree of even distribution of the injected
material.
It is the general object of this invention to provide a process and
a nozzle for injection of an aqueous solution of a salt obtaining a
stable and well distributed injection. The injection aimed at must
be able to operate under all conditions without interruptions
caused by blocking of the nozzle. Simultaneously, it must operate
with a high degree of even distribution of the sprayed fluid in the
gas, which it is sprayed into.
A process and a nozzle have now been found, so that when the nozzle
is designed in accordance with the invention, a urea solution can
be sprayed into exhaust gas from a vehicle obtaining a very even
distribution in the exhaust gas. A nozzle of the invention operates
for a long period without blocking the nozzles.
SUMMARY OF THE INVENTION
The invention is a method and apparatus for uniformly injecting a
fluid stream into a gas stream at elevated temperature by means of
an injection nozzle comprising a nozzle head and a supply inner
tube being concentrically surrounded with an outer casing tube
spaced apart from the inner supply tube. It comprises passing the
fluid stream through the inner tube and the nozzle head and
maintaining temperature of the fluid stream in the inner tube by
providing thermal insulation in at least part of an annular space
between the inner tube and the outer tube. Further, it comprises
maintaining a constant flow of the fluid inside the inner tube and
nozzle head by plugging the nozzle head at outlet end and spraying
the fluid stream through a number of nozzle holes provided in the
nozzle head adjacent to the outlet end of the nozzle head. It also
comprises spraying the fluid stream through the nozzle holes in a
direction being substantially at right angles to flow direction of
the gas stream and adjacent to center axis of the gas stream
channel, and finally uniformly distributing the sprayed fluid
stream into the gas stream by a conical narrowing of the outer
casing tube in region adjacent to the nozzle head.
The preferred insulating material is ceramic and formed from a thin
layer of the material and rolled up to a desired shape using
organic glue.
The inner tube may be equipped with a 90.degree. bend between the
end of the outer tube and the end of the inner tube.
The fluid can be a mixture of air and an aqueous solution of urea
with 20-50% urea by weight, preferable 30-35% and most preferred
32.5% urea by weight.
The invention is particularly useful for uniform distribution of an
aqueous solution of urea sprayed into a hot diesel exhaust gas,
where water might boil off resulting in urea crystallisation.
Especially advantageous is the invention in big vans and
lorries.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross section of a straight nozzle according to the
invention.
FIG. 2 is a cross section of nozzle with a 90.degree. bend
according to the invention.
FIG. 3 is a cross section of an exhaust pipe with a nozzle
according to the invention.
FIG. 4 is a frontal section of nozzle with a 90.degree. bend
according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
In diesel engine driven vehicles combustion takes place with a
certain amount of excess air. This results in formation of nitrogen
oxides, NO.sub.x in the exhaust gas, which is a serious pollution
for the environment.
NO.sub.x can be reduced by ammonia, NH.sub.3, which is difficult to
store in vehicles, and an aqueous solution of urea,
H.sub.2NCONH.sub.2, is therefor used as a reducing agent.
The ammonia is formed when urea decomposes as it is sprayed out and
mixed with the hot exhaust gas according to the following reaction:
H.sub.2NCONH.sub.2+H.sub.2O.fwdarw.2NH.sub.3,+CO.sub.2
Urea decomposes completely only if the temperature exceeds
200.degree. C. Thus 200.degree. C. is the lowest temperature at
which urea can be injected to the exhaust gas.
The mixture of exhaust gas and reductant, ammonia, then passes over
a catalyst where the nitrogen oxides, nitrogen monoxide, NO and
nitrogen dioxide, NO.sub.2 reacts with the ammonia to form nitrogen
and water according to the following reactions:
4NO+4NH.sub.3+O.sub.2.fwdarw.4N.sub.2+6H.sub.2O, and
6NO.sub.2+8NH.sub.3.fwdarw.7N.sub.2+12H.sub.2O
During normal operation the exhaust gas shall and will be hot,
simultaneously it is important that the urea solution inside the
injection nozzle does not exceed the temperature where water will
evaporate resulting in crystallisation of urea and blockage of
injection nozzle.
The invention provides furthermore a nozzle for urea solution/air
mixture injection into a hot exhaust gas without crystallisation of
urea. The injection nozzle comprises an outer casing tube, a
coaxial supply inner tube and an insulation material in the annular
space between the two tubes. This prevents the hot exhaust gas to
heat up the aqueous urea solution to the temperature, where water
evaporates and urea crystallises.
In the outlet region, the inner tube is equipped with a nozzle head
with plug. Very close to the plug, nozzle holes are positioned.
This ensures a flow of solution in the entire volume of the inner
tube, so "dead volume" is avoided, which otherwise would heat up
resulting in urea crystallisation. The plug may be removed for
cleaning the inner tube.
By this nozzle tip design, the solution can flow out in a right
angle to the axis of the nozzle ensuring a good distribution and
without risk of formation of solid urea and blocking the
nozzle.
As soon as the urea solution/air mixture flows out through the
nozzle holes, an aerosol is formed. When the hot exhaust gas heats
the aerosol, the urea is converted to ammonia, and the ammonia
reduces nitrogen oxides in the exhaust to nitrogen over a catalyst
installed downstream of the nozzle.
As the catalyst is installed in the entire cross sectional area of
an enlarged part of the exhaust gas pipe, uniform distribution of
urea/ammonia in the pipe is very important for the conversion of
nitrogen oxides.
The performance and design of the invention is made further clear
by the below description of the drawings.
One preferred embodiment of the invention is disclosed on FIG. 1,
where a straight injection nozzle is shown. The nozzle comprises a
nozzle head 1, an outer casing tube 2 and a coaxial supply inner
tube 3, where the annular space between the tubes is filled with an
insulating material 4. The insulating material 4 is formed as a
solid annulus and is fitted between the inner tube 3 and the outer
tube 2.
The end of the nozzle head 1 is a screw 5 having a flat end. Just
next to the flat end the nozzle holes 6 are drilled, which
eliminates nozzle volume without flow. The outer tube ends with a
conical part 7 with the narrow part close to inner tube 3 adjacent
to nozzle head 1. The urea solution/air mixture 8 flows through the
inner tube 3 maintaining the low temperature, where no water
evaporates and no urea crystallises. The mixture 8 flows out
through the nozzle holes 6, where an aerosol is formed. In the hot
exhaust gas the urea solution is converted to ammonia and carbon
dioxide.
Another preferred embodiment of the invention is shown on FIG. 2,
which in principle is equal to the above injection nozzle except
for the nozzle head, which is provided with a 90.degree. bend 10,
where 5 mm between the bend and the nozzle holes 6 are
straight.
A preferred mode of installation is shown on FIG. 3. A nozzle with
a 90.degree. bend is inserted in a right angle through the wall of
the exhaust gas pipe 11 the tip points in the exhaust gas flow
direction and is coaxially installed in the middle of the exhaust
gas pipe 11. In this way the urea solution flows out through the
nozzle holes 6 at a right angle to the exhaust gas flow direction
and in the middle of it, which results in the very good
distribution.
When sprayed through the nozzle holes 6, the aqueous urea solution
is converted to ammonia and carbon dioxide; this and the exhaust
gas flow to a catalyst 12, where ammonia converts nitrogen oxides
to nitrogen and water. Optimal conversion over the catalyst is only
obtained by proper distribution of ammonia in the exhaust gas
pipe.
FIG. 4 shows the position of the nozzle holes when the injection
nozzle is equipped with four nozzle holes. When they are drilled
45.degree. from vertical direction, the vertical part of the
injection nozzle will not disturb the exhaust gas flow coming from
behind the injection nozzle.
The invention has particular use in diesel engine driven ships,
trains, vans, lorries and similar, where the above toxic gases are
formed and must be removed in order not to pollute the atmosphere.
Removal of toxic gases will be a government requirement in an
increasing number of countries, as the gases are harmful to human
beings, animals and even buildings.
EXAMPLES
The dimensions of the injection nozzle are important to obtain a
uniform distribution of ammonia in the exhaust gas pipe.
One preferred embodiment of the invention is manufactured with
dimensions as below. The dimensions correspond to air and solution
flows/consumption also given below and these figures correspond to
use of the invention in an ordinary van with diesel driven
engine.
When operating the engine, an air-flow of 20 Nl/min is appropriate.
The urea solution consumption is adjusted to correspond to the
NO.sub.x content in the exhaust gas, however, a flow of 7.5 l/hr
solution is typical. The aqueous urea solution has a concentration
of 20-50% as weight preferably, 30-35% and most preferred 32.5 wt %
urea.
The inner tube of the corresponding injection nozzle has an outer
diameter of 6 mm and a wall thickness of 1.5 mm, and the outer tube
has an outer diameter of 25 mm and a wall thickness of 1.22 mm and
a ceramic material is fitted between the tubes. The nozzle is
equipped with four holes each with a diameter of 0.55 mm and
equally spaced. For other flows the number and size of holes are
adjusted accordingly, often eight holes with a diameter of 0.39 mm
are used.
In a specific embodiment of the invention, the inner surface of the
conical part 7 has an angle of 30.degree. and the length of the
conical part is 44.4 mm. These dimensions have proved to give a
very good distribution of the reducing medium in the exhaust
gas.
The insulating material in the space between the tubes is a ceramic
material, which is rolled to the desired shape and kept in the
shape by an organic binder. The ceramic material is commercially
available under the name "Isovac" from Keramax a/s, Tollose,
Denmark.
Apart from the insulating material a suitable construction material
for the nozzle is stainless steel SS 316.
Test Results
The nozzle of the invention has proved to be particular useful when
employing aqueous solutions of urea which are sprayed into hot
exhaust gas, especially nitrogen oxides containing diesel exhaust
gas.
A Urea Selective Catalytic Reduction system was installed in
September 2003 for a field test in a bus with a 4 L 150 hp diesel
engine. The nozzle used for injection of urea was at the beginning
of the field test just a pipe without any insulation. The bus was
operating in real conditions in London city traffic.
After a short period of 2 working days, the system was found not to
work. The reason was found to be urea clogging in the nozzle.
The nozzle was cleaned mechanically and the system was once again
operational.
After 2 more days the nozzle was once again completely clogged by
urea residues.
The conventional nozzle was replaced with a nozzle to the Haldor
Topsoe A/S nozzle according to the invention with insulation around
the injection pipe.
The system has then been running a total of 5 months of operation
without any clogging problems.
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